Something broke down in the internal systems. It is still unclear quite what, though it has been blamed on a router (a piece of equipment which directs internet data in or across a network). RIM later called it a "core switch failure".

Even a momentary lapse in the flow of RIM's data could be calamitous: the Guardian understands the Slough NOC servers normally deal with 8 gigabytes of data every second – equivalent to 16 hours of BBC iPlayer TV viewing. In a typical month, the unassuming two-storey building in Slough sees up to 20 petabytes, or 20m gigabytes, pass through it.

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"RIM grew in popularity too quickly, and got complacent over the iPhone," one former staffer with close knowledge of its network setup told the Guardian.

He said that rather than rewrite its core networking software so that it could deal with the rapid boom in the smartphone market after 2005, RIM tried simply to increase the number of servers running the software, and spread demand among them

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The reason why the amount of data passing through Slough is so colossal is that it is one of just four NOCs maintained by RIM to route data between all its global users – and it serves almost everyone in Europe, the Middle East, Africa and India. It also handles all of the GPRS "packets" – data sent worldwide via low-speed phone networks – to BlackBerry devices.

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The real point of failure appears to be a fundamental piece of RIM's own software called the "Relay" which directs traffic within each of the four NOCs.